The extremely halophilic archaeon Natrialba aegyptiaca secretes the L-homo type of poly-g-glutamate (PGA) as an extremolyte. We examined the enzymes involved in glutamate metabolism and verified the presence of L-glutamate dehydrogenases, L-aspartate aminotransferase, and L-glutamate synthase. However, neither glutamate racemase nor D-amino acid aminotransferase activity was detected, suggesting the absence of sources of D-glutamate. In contrast, D-glutamate-rich PGA producers mostly possess such intracellular sources of D-glutamate. The results of our present study indicate that the D-glutamate-anabolic enzyme “glutamate racemase” is pivotal in the biosynthesis of PGA.
References
[1]
Shimada, A.; Ozaki, H. Flexible enantioselectivity of tryptophanase attributable to benzene ring in heterocyclic moiety of D-tryptophan. Life？2012, 2, 215–228, doi:10.3390/life2020215.
Bada, J.L.; Miller, S.L. Racemization and the origin of optically active organic compounds in living organisms. Biosystems？1987, 20, 21–26, doi:10.1016/0303-2647(87)90016-5.
[4]
Ashiuchi, M.; Misono, H. Poly-γ-glutamic acid. In Biopolymers; Fahnestock, S.R., Steinbüchel, A., Eds.; Wiley-VCH: Weinheim, Germany, 2002; Volume 7, pp. 123–174. Chapter 6.
[5]
Ashiuchi, M. Occurrence and biosynthetic mechanism of poly-γ-glutamic acid. In Microbiol. Monogr.: Amino-Acid Homopolymers Occurring in Nature; Hamano, Y., Ed.; Springer-Verlag: Heidelberg, Germany, 2010; Volume 15, pp. 77–94.
[6]
Yamasaki, D.; Minouchi, Y.; Ashiuchi, M. Extremolyte-like applicability of an archaeal exo-polymer, poly-γ-L-glutamate. Environ. Technol.？2010, 31, 1129–1134, doi:10.1080/09593331003592279.
[7]
Lentzen, G.; Schwarz, T. Extremolytes: natural compounds from extremophiles for versatile applications. Appl. Microbiol. Biotechnol.？2006, 72, 623–634, doi:10.1007/s00253-006-0553-9.
[8]
Ashiuchi, M.; Soda, K.; Misono, H. A poly-γ-glutamate synthetic system of Bacillus subtilis IFO 3336: Gene cloning and biochemical analysis of poly-γ-glutamate produced by Escherichia coli clone cells. Biochem. Biophys. Res. Commun.？1999, 263, 6–12, doi:10.1006/bbrc.1999.1298.
[9]
Ruzheinikov, S.N.; Taal, M.A.; Sedelnikova, S.E.; Baker, P.J.; Rice, D.W. Substrate-induced conformational changes in Bacillus subtilis glutamate racemaseand their implications for drug discovery. Structure？2005, 13, 1707–1713, doi:10.1016/j.str.2005.07.024.
[10]
Lundqvist, T.; Fisher, S.L.; Kern, G.; Folmer, R.H.A.; Xue, Y.; Newton, D.T.; Keating, T.A.; Alm, R.A.; De Jonge, B.L.M. Exploitation of structural and regulatory diversity in glutamate racemases. Nature？2007, 447, 817–822, doi:10.1038/nature05689.
[11]
Kimura, K.; Tran, L.-S.P.; Itoh, Y. Roles and regulation of the glutamate racemase isogenes, racE and yrpC, in Bacillus subtilis. Microbiology？2004, 150, 2911–2920, doi:10.1099/mic.0.27045-0.
[12]
Kimura, K.; Tran, L.-S.P.; Uchida, I.; Itoh, Y. Characterization of Bacillus subtilis γ-glutamyltrans-ferase and its involvement in the degradation of capsule poly-γ-glutamate. Microbiology？2004, 150, 4115–4123, doi:10.1099/mic.0.27467-0.
[13]
Sambrook, J.; Fritsch, E.F.; Maniatis, T. Molecular Cloning: A Laboratory Manual, 2nd ed. ed.; Cold Spring Harbor Laboratory: Cold Spring Harbor, NY, USA, 1989.
[14]
Ashiuchi, M.; Kamei, T.; Baek, D.-H.; Shin, S.-Y.; Sung, M.-H.; Soda, K.; Yagi, T.; Misono, H. Isolation of Bacillus subtilis (chungkookjang), a poly-γ-glutamate producer with high genetic competence. Appl. Microbiol. Biotechnol.？2001, 57, 764–769, doi:10.1007/s00253-001-0848-9.
[15]
Ashiuchi, M.; Shimanouchi, K.; Nakamura, H.; Kamei, T.; Soda, K.; Park, C.; Sung, M.-H.; Misono, H. Enzymatic synthesis of high-molecular-mass poly-γ-glutamate and regulation of its stereochemistry. Appl. Environ. Microbiol.？2004, 70, 4249–4255, doi:10.1128/AEM.70.7.4249-4255.2004.
[16]
Ashiuchi, M. Analytical approaches to poly-γ-glutamate: Rapid quantification, molecular size determination, and stereochemistry investigation. J. Chromatogr. B？2011, 879, 3096–3101, doi:10.1016/j.jchromb.2011.03.029.
